1. Field of the Invention
The present invention relates to a condensed water discharging apparatus for a fuel cell system, and more particularly, to condensed water discharging apparatus for a fuel cell system which serves to separate the water generated at an anode and drain it so as to prevent the condensed water from being recirculated with unused hydrogen during hydrogen recirculating process.
2. Description of the Related Art
In general, a fuel cell system generates electricity using hydrogen and oxygen in the air, and this fuel cell system may be used as a power source of a vehicle.
A fuel cell system comprises a separator, an anode, an electrolyte membrane, a cathode, a hydrogen/air/cooling water distributing structure, an anode flow field, a cathode flow field, and a cooling flow field.
When a fuel cell system is driven, hydrogen is supplied from a hydrogen tank to an anode flow field of a fuel cell system through a hydrogen supplying solenoid valve and a pipe.
In order to increase efficiency of hydrogen as a fuel, non-reacted hydrogen is recirculated. This procedure is performed such that a hydrogen recirculation blower is operated in a state that a purge valve is closed, non-reacted hydrogen in a fuel cell system moves along a pipe and goes into an anode flow field of a fuel cell system through a hydrogen recirculation blower and a hydrogen recirculation blocking valve.
A hydrogen purge value is configured to be opened at a periodically predetermined time to discharge nitrogen and water which come through an electrolyte membrane.
Air is supplied from the atmosphere to an air blower through a pipe, and an air blower controls an air flow rate according to a driving condition so that air is supplied to a cathode flow field of a fuel cell system through a pipe.
Hydrogen (H2) at an anode flow field dissociates into positive hydrogen ions and negatively charged electrons, in which the hydrogen ions are conducted through an electrolyte membrane to the cathode. O2 at a cathode flow field dissociates to O— ions by catalyst, and the positive hydrogen ions and O— ions react to form H2O.
Meanwhile, in a conventional fuel cell system vehicle, condensation of vapor occurs in a cathode as well as in an anode according to a driving condition, and condensed water needs to be removed to improve durability, lifespan and performance of a fuel cell system.
Water generated in an anode is discharged from a fuel cell system stack system to be transferred to a hydrogen recirculation blower and is then mixed with pure hydrogen which comes out of a hydrogen tank before going into an anode flow field of a fuel cell system stack again.
By the above described method, waste of hydrogen can be avoided, resolving a security problem occurred when hydrogen is discharged to the air.
However, hydrogen discharged from a fuel cell system stack contains water inevitably generated in a fuel cell system. A vapor form does not cause any problem, but condensed water inevitably generated according to a driving condition causes many problems.
If condensed water generated in a hydrogen side (i.e., anode) goes to a recirculation blower, a recirculation blower causes overload, so that flooding occur at an entrance of a fuel cell system stack system, thereby fatally degrades durability of a fuel cell system stack and a recirculation blower.
Also, if hydrogen is discharged to the air together with condensate water, there occurs a dangerous safety problem in a vehicle, and thus hydrogen should not be discharged into the ambient air.
In order to resolve the above problem, a conventional fuel cell system vehicle employs a water discharging apparatus for removing condensed water using gravity.
FIG. 1 is a perspective view illustrating a conventional water discharging apparatus. The conventional water discharging apparatus is arranged in an engine room together with a fuel cell system. The conventional water discharging apparatus of FIG. 1 comprises a housing 3, a solenoid valve 4 installed in the outlet portion 2 to adjust a flow rate, and water level sensors 5 and 6 for sensing a water level of condensed water in the housing 3. The housing 3 has an inlet portion 1, arranged in its upper portion, through which condensed water flows in and an outlet portion 2, arranged in its lower portion, through which condensed water is discharged.
The housing has the total length of 185 mm and the total volume of 680 ml, and as the water level sensors, a high water level sensor 5 installed in an upper portion of the housing 3 and a low water level sensor 6 installed in a lower portion of the housing 3 are provided.
When condensed water flowing in through the inlet portion 1 of the housing 3 reaches a level of the high water level sensor 5, the solenoid valve 4 is opened to discharge condensate water, and when condensed water is lowered to a level of the low water level sensor 6, the solenoid valve 4 is closed not to discharge condensed water any more, whereby it is possible to remove condensed water contained in recirculated hydrogen and to prevent hydrogen from being discharged to the air.
If a fuel cell system is employed in a vehicle such as a sedan later, a fuel cell system should be arranged on a floor of a vehicle. However, in this instance, it is difficult to apply the existing water discharging apparatus which removes condensed water by using gravity “as is”.
The reason why the existing water discharging apparatus can not be applied in case where a fuel cell system is arranged on a floor of a vehicle is described below in detail.
FIG. 2 is a schematic view illustrating a ground clearance when a fuel cell system stack 8 is mounted on a central floor 7 of a sedan type vehicle. In case of a sedan type vehicle, a ground clearance of FIG. 2 could be improved later, but the improvement range is limited. A reference numeral 9 denotes a hydrogen tank.
In this instance, a ground clearance is merely 170 mm, i.e., the distance from the lowest surface of the fuel cell system stack 8, and so it is difficult to use the existing water discharging apparatus having the total length of 185 mm. Since the existing water discharging apparatus uses gravity to discharge water, water can be discharged from the fuel cell system stack by gravity only when it is arranged below the lowest surface of the fuel cell system stack 8. In order to remove condensed water by using gravity in a sedan type vehicle of FIG. 2, a ground clearance should be lowered to less than 150 mm, but the existing water discharging apparatus can secure merely the height of about 20 mm.
Even though the existing water discharging apparatus is modified, it is almost impossible to secure an enough ground clearance because of the length of 185 mm.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.